Selective charging magnitude compensation

ABSTRACT

In an ink drop printer, the charge on a just formed drop is stored and used to provide a compensating charge for the next drop, to be formed in order to avoid the adverse effects of the charge on the just formed drop.

[111 3,827,057 [451 July 30, 1974 SELECTIVE CHARGING MAGNITUDECOMPENSATION Inventors: Vincent E. Bischoff, River Grove; Robert I.Keur, Niles, both of Ill.

Assignee: A. B. Dick Company, Chicago, Ill. Filed: Jan. 2, 1973 Appl.No.: 320,325

Primary Examiner.loseph W. Hartary Attorney, Agent, or Firm'-Lindenberg,Freilich, Wasserman, Rosen & Fernandez [57] ABSTRACT In an ink dropprinter, the charge on a just formed [52] US. Cl. 346/75 rop is storedand used to provide a compensating [51] Int. Cl. G01d 18/00 charge o thnext p, to be formed i order to [58] Field of Search 346/75 avoid th adrs ffe ts f th charg n the just formed drop. [56] References CitedUNITED STATES PATENTS 8 Claims, 2 Drawing Figures 3,631,511 l2/l97lKeuretal. 346/75 DE A Vl DEO comp comp ANAL GEN NETWORK I I I A E) C 2058 GAIN g ES Q" CONTROL C NETWORK [30 V {32 {54 V DAT-A CHARACTER VlDVlD SOURCE GEN PRoc AMP l6 24A 0) K g 22 b INK g 4 g Q o REJERVOWTRANSDUCER 6 o 0 Q o G VOLTA6E CATCHER PATENTEBJuLamsm v) DEO com D QQMPANAL GEN NETWORK I A-Elvc pa GAIN SYSTEM CONTROL CLOCK NETWORK PO P2 {54r 40 DATA CHARACYER WD 5 v19 SOURCE GEN p AMP \6 \O) \2 /\g 22 EL-5223M;\4 I I4 Q INK RE ERVO\R TRANSDUCER 5 0 o a 6 0 24B. 2 H\G:H -n 28VOLTAGE CATCHER f? 1 W5 fi CLOCK G FF \/\D K Q FF v ,54 6O 50 B Q 72 62C Q56 74 c o L CK- DELAY FF I BACKGROUND OF THE INVENTION The presentinvention relates to ink drop printing apparatus, and more particularly,to an improved arrangement for charging drops.

In a U.S. Pat. No. 3,631,511, it was shown that one of the problemswhich arises in ink drop printing apparatus is that a drop which ischarged, and which is just broken from the-ink jet stream has anelectric field which operates on the immediately following drop beingformed and charged in a manner to depress or lower the charge, whichthat drop will receive from the video signal. Similar, but lesser degreeeffects are caused by the drops which precede the one justbroken fromthe ink jet stream. As a result, the following ink drop is not properlydeflected by the following electric field. This results in printingwhich is not as good as it should be, or which is imprecise with respectto character formation. In order to avoid these effects, increased dropspacing, as well as guard drops, that is, drops with no charge, are usedfor spacing charged drops. These techniques however slow up the printingprocess or have undesirable effects.

U.S. Pat. No. 3,631,511, proposes an arrangement for compensating forthe effects on a drop being formed, of a charge on the drop which hasjust been formed by detecting whether or not a just formed drop has hada charge applied to it, and if it has, then a compensating voltage isadded to the video charging voltage being applied to charge the nextdrop being formed, whose amplitude varies with the amplitude of thecharging voltage. This arrangement does charge, but since the chargeapplied to a drop does vary, it does not completely and/or accuratelycompensate for the adverse effects of the charge of a just formed dropon the next drop being formed.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is tocompensate accurately the charge to be applied to a drop being chargedfor the effects of a charge on a drop which has already been formed andcharged.

Yet another object of the present invention is the provision of anarrangement for improving the printing quality and speed of an ink dropprinter.

These and other objects of the present invention are achieved in anarrangement wherein means are provided for storing the fact that a videosignal has been applied to a just formed drop, together with theamplitude of that video signal. In that event, a compensating charge isapplied to the succeeding drop being formed, which is determined be theamplitude of the charge on the already formed drop, to therebyaccurately compensate for the effects of the charge, on the alreadyformed drop.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will best be understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block schematic diagramillustrative of this invention in an ink drop printing arrangement FIG.2 is a schematic block diagram of an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagramof a known type of ink jet printer, which also includes a schematicrepresenta tion of the circuitry required, in accordance with thisinvention.

An ink jet printer, basically includes an ink reservoir 10, which holdsink under pressure. A pipe 12, discharges the ink from the ink reservoirin the form of a stream 14, which is directed at writing paper 16. Anelectromechanical transducer 18 squeezes the nozzle at a frequencydetermined by the output of the sync signal generator or system clock20. The periodic nozzle squeezing causes periodic narrowing or neckingof the ink jet 14, so that drops 14 are formed along the path of the inkjet stream on its way to the paper 16. These drops are substantiallyuniformly sized and regularly spaced. A small ring 22 is placed at adrop charging location along the ink jet 14, where it begins to breakinto drops. The drops are formed within the ring and pass out of itthrough an electric field, which is established by two spaced plates,respectively 24A and 243. A high voltage deflection field is establishedbetween these plates from a high voltage source 26. Drops which are notused in the process of writing on the paper, are not charged and arecaught by a waste catcher 28. The charged drops are deflected betweenthe plate 24A and 243, in a manner so they avoid the waste catcher andare directed upon the paper at a location determined by the amplitude ofa charge on a drop.

Information for charging the drops, which determines what characters areprinted on the paper 16, is provided by video signals from a data source30. These signals may be digital or analog in form. They are applied toa character signal function generator 32, at a rate determined by theoutput of the system clock 20. The binary character signal fucntiongenerator 32, processes its input in binary digital form, finallyconverting the digital signals into a series of electric signals whichrepresent the voltages to be successively used to charge successivedrops. These voltages are applied to a video processor 34, whichconverts a signal to a form suitable for charging the drops so that theywill be deposited in a desired pattern on the paper. The output of thevideo processor is applied to a video amplifier 40.

The character being printed is usually constructed by deflecting thedrops vertically and moving the paper horizontally, or by moving theentire ink jet printing horizontally, the paper being stationary and thedrops being deflected vertically as the ink jet printing assembly ismoved. In either event, the signals out of the character generatorcomprise a sequence of voltages whose amplitudes are determined by thecharacter desired to be printed.

In accordance with this invention, a digital output (represented by A,B, and C) is taken from the character generator. The character generatorusually includes a Y column counter which converts the video signalreceived from the data source 20 into a digital count. This digitalcount, here represented as A, B, and C, constitutes the desired discretecharge levels for the droplets. The charge level is applied to the videoprocessor 34, the A, B, and C digital count is applied to the Referringto FIG. 2, there, shown in more detail, is a schematic representation ofwhat is included in blocks 36, 44 and 46 of FIG. 1. The video analyzer46 indicates whether a particular drop is to be compensated based uponwhether a previous drop was charged. The video analyzer comprises a I, Kflip-flop with video signals applied to its K input and video signals toits .I input. It also has a clock input. The Q output of the analyzer 46is connected as the enabling inputs to NAND gates 58, 60, and 62.

In the presence of a video signal being applied to the video processor,the flip-flop 46 is reset with its Q output high. In the absence of sucha video signal, a video" signal is applied to the J input of theflip-flop and its Q output goes high.

Three data storage registers or, flip-flops 52, 54 and 56 have theirrespective Q outputs connected, as second required inputs, to the NANDgates. One input to each of the flip-flops 52, 54 and 56 is a clocksignal, which is applied through a delay circuit 57, the other inputsare the respective binary signal inputs A, B and C. The data on lines A,B, and C are entered in the re spective flip-flops toward the trailingend of a system clock pulse as a result of the time delay caused by thedelay circuit 45. This data is stored thereby, and will be availableduring the next or successive drop formation period.

The compensation network 36, includes a ladder of binary weightedresistors respectively 70, 72 and 74, to which the respective outputs ofNAND gates 58, 60 and 62 are connected. The other ends of resistors 70,72 and 74 are commonly connected to a compensation magnitude controlpotentiometer 50. The NAND gates function as current switches. Theseswitches are selected by the outputs of the flip-flops 52, 54 and 56.

The gain of the video amplifier 40, is controlled by the compensationnetwork 36 as follows. As more of the gates 58, 60, and 62 are enabled,the compensation network actuates the gain control network 38 toincrease the gain of the video amplifier 40. A reduction in the numberof gates 58, 60, and 62 enabled, operates to reduce the gain of thevideo amplifier 40.

From what has been described thus far, it will be understood that uponthe trailing edge portion of a clock pulse the video signal, if any,being used to charge a drop being formed is stored in flip-flop 52, 54and 56. In the event the succeeding drop is to be charged, when the nextvideo signal arrives, flip-flop 46 serves to enable gates 58, 60 and 62whereby the gain of the video amplifier 40 is established so that theamplitude of the charge which will be applied to the drop then beingformed is the video signal amplified sufficiently to includecompensation for the charge applied to the preceding drop. In theabsence of a gain control voltage which occurs when no charge is appliedto the preceding drop, the gain factor of the video amplifier is set atsome nominal value, whereby no compensation is applied to the videovoltage which is being used to charge a drop. It can be appreciated fromthe foregoing, that the present invention generates a gain controlvoltage which represents a function identical to the video amplifiercharging function, delayed in time by one drop period. This is an analogfunction of the preceding drop charge which is then used to determinethe gain to be given to the video signal intended for use as the nextdrop charge.

There has accordingly been described and shown herein a novel and usefularrangement for establishing the amplitude of a charge to be applied toa drop which includes compensation for the value of the charge which wasapplied to an immediately preceding drop.

What is claimed is:

1. In an ink drop system, an arrangement for compensating the charge tobe applied to a drop being formed to correct for the effects of thecharge on a drop which was just previously formed comprising:

means for storing a representation of a voltage which was used to chargea drop which was just previously formed, and

means for amplifying a voltage to be applied to charge the next drop tobe formed following said previously formed drop by an amount which is afunction of said stored representation of a voltage to thereby provide avoltage for charging said next drop which includes compensation for thecharge on said drop which was previously formed.

2. In an ink drop system as recited in claim 1 wherein there isincluded:

means for sensing that said next drop to be formed is to be charged andproviding an output indicative thereof, and

means, enabled responsive to said output, to convert said representationof a voltage in said means for storing into said function forcontrolling the gain of said means for amplifying.

3. In an ink drop system, an arrangement for compensating a charge to beapplied to a drop being formed to correct for the effects of the chargeon a drop which was just previously formed comprising video signal meansfor providing an output comprising a representation of a voltage usedfor charging each drop,

means for storing an output of said video signal means comprising arepresentation of the voltage which was used to charge a drop which wasjust previously formed,

means for sensing that a representation of a voltage is being providedby said video signal means to charge a drop being formed immediatelyfollowing said just previously formed drop and providing an outputindicative thereof,

first means, enabled responsive to said output from said means forsensing, for converting said representation of a voltage stored by saidmeans for storing into a representative gain control voltage, and

second means for converting said representation of a voltage used forcharging a drop immediately following said just previously formed dropinto a drop charging voltage,

amplifier means for amplifying said drop charging voltage, beingprovided by said second means for converting, by an amount determined bysaid representative gain control voltage to thereby compensate for theeffects of the charge on the just previously formed drop.

4 In an ink drop printer as recited in claim 3 wherein said means forstoring comprises:

flip-flop means for storing a digital representation of the voltage usedto charge the previously charged drop,

said means for converting, enabled responsive to an output from saidmeans for sensing comprises: gate means connected to receive outputsfrom said means for storing and said means for sensing, and

resistor means connected to receive output from said gate means forconverting said output from said gate means into a representative gaincontrol voltage.

5. In an ink drop printing means as recited in claim 4 wherein saidmeans for sensing comprisesa flip-flop having a first output responsiveto a voltage being applied thereto from said video signal means and asecond output when no voltage is applied thereto from said video signalmeans, and

means connecting said first output to said gate means.

6. In an ink drop printing system, an arrangement for compensating thecharge to be applied to a drop being formed to correct for the effectsof the charge on a drop which was just previously formed comprising:

character generator means for providing analog signals for chargingdrops and a digital signal representative of each analog signal,

means for storing a digital signal representative of an analog signalused to charge the drop which was previously formed,

means for sensing that an analog signal is being provided by said videosignal means for charging a drop being formed and providing an outputindicative thereof,

gate means connected to receive output from said means for storing andenabled responsive to an output from said means for sensing forconverting said digitalsignal stored in said means for storing into ananalog control signal,

drop charge amplifying means to which analog signals from said charactergenerator are applied for amplifying said analog signals for applicationfor charging a drop being formed, and

means for controlling the gain of said drop charge amplifying meansresponsive to said analog control signal whereby said output of saiddrop charge amplifying means is an analog signal for charging a dropbeing formed compensated for the charge applied to a just previouslycharged drop.

7. In an ink drop system, the method of compensating the charge to beapplied to a drop being formed to correct for the effects of a charge ona drop which was just previously formed, comprising the steps of:

storing a voltage representative of the charge applied to said justpreviously formed drop until the next drop is being formed, and

amplifying a voltage to be applied to charge said next drop by an amountwhich is a function of said stored voltage representative of the chargeapplied to said just previously formed drop to provide a voltage tocharge said next drop which is compensated for the charge on said justpreviously formed drop.

8. The method recited in claim 7 wherein there is included the steps of:

sensing that the next drop being formed following said just previouslyformed drop is to be charged and providing an output indicative thereof,and converting the stored voltage representative of the charge appliedto said just previously formed drop in the presence of said output intoa function for controlling amplification.

1. In an ink drop system, an arrangement for compensating the charge tobe applied to a drop being formed to correct for the effects of thecharge on a drop which was just previously formed comprising: means forstoring a representation of a voltage which was used to charge a dropwhich was just previously formed, and means for amplifying a voltage tobe applied to charge the next drop to be formed following saidpreviously formed drop by an amount which is a function of said storedrepresentation of a voltage to thereby provide a voltage for chargingsaid next drop which includes compensation for the charge on said dropwhich was previously formed.
 2. In an ink drop system as recited inclaim 1 wherein there is included: means for sensing that said next dropto be formed is to be charged and providing an output indicativethereof, and means, enabled responsive to said output, to convert saidrepresentation of a voltage in said means for storing into said functionfor controlling the gain of said means for amplifying.
 3. In an ink dropsystem, an arrangement for compensating a charge to be applied to a dropbeing formed to correct for the effects of the charge on a drop whichwas just previously formed comprising video signal means for providingan output comprising a representation of a voltage used for chargingeach drop, means for storing an output of said video signal meanscomprising a representation of the voltage which was used to charge adrop which was just previously formed, means for sensing that arepresentation of a voltage is being provided by said video signal meansto charge a drop being formed immediately following said just previouslyformed drop and providing an output indicative thereof, first means,enabled responsive to said output from said means for sensing, forconverting said representation of a voltage stored by said means forstoring into a representative gain control voltage, and second means forconverting said representation of a voltage used for charging a dropimmediately following said just previously formed drop into a dropcharging voltage, amplifier means for amplifying said drop chargingvoltage, being provided by said second means for converting, by anamount determined by said representative gain control voltage to therebycompensate for the effects of the charge on the just previously formeddrop. 4 In an ink drop printer as recited in claim 3 wherein said meansfor storing comprises: flip-flop means for storing a digitalrepresentation of the voltage used to charge the previously chargeddrop, said means for converting, enabled responsive to an output fromsaid means for sensing comprises: gate means connected to receiveoutputs from said means for storing and said means for sensing, andresistor means connected to receive output from said gate means forconverting said output from said gate means into a representative gaincontrol voltage.
 5. In an ink drop printing means as recited in claim 4wherein said means for sensing comprises a flip-flop having a firstoutput responsive to a voltage being applied thereto from said videosignal means and a second output when no voltage is applied thereto fromsaid video signal means, and means connecting said first output to saidgate means.
 6. In an ink drop printing system, an arrangement forcompensating the charge to be applied to a drop being formed to correctfor the effects of the charge on a drop which was just previously formedcomprising: character generator means for providing analog signals forcharging drops and a digital signal representative of each analogsignal, means for storing a digital signal representative of an analogsignal used to charge the drop which was previously formed, means forsensing that an analog signal is being provided by said video signalmeans for charging a drop being formed and providing an outputindicative thereof, gate means connected to receive output from saidmeans for storing and enabled responsive to an output from said meansfor sensing for converting said digital signal stored in said means forstoring into an analog control signal, drop charge amplifying means towhich analog signals from said character generator are applied foramplifying said analog signals for application for charging a drop beingformed, and means for controlling the gain of said drop chargeamplifying means responsive to said analog control signal whereby saidoutput of said drop charge amplifying means is an analog Signal forcharging a drop being formed compensated for the charge applied to ajust previously charged drop.
 7. In an ink drop system, the method ofcompensating the charge to be applied to a drop being formed to correctfor the effects of a charge on a drop which was just previously formed,comprising the steps of: storing a voltage representative of the chargeapplied to said just previously formed drop until the next drop is beingformed, and amplifying a voltage to be applied to charge said next dropby an amount which is a function of said stored voltage representativeof the charge applied to said just previously formed drop to provide avoltage to charge said next drop which is compensated for the charge onsaid just previously formed drop.
 8. The method recited in claim 7wherein there is included the steps of: sensing that the next drop beingformed following said just previously formed drop is to be charged andproviding an output indicative thereof, and converting the storedvoltage representative of the charge applied to said just previouslyformed drop in the presence of said output into a function forcontrolling amplification.